The benthos in Lake Oahe, as determined from about 450 bottom samples collected during the open water season in 1968 and 1969, was dominated by oligochaetes and chironomids; Caenis (Ephemeroptera) and Chaoborus (Diptera) were occasionally abundant. Total benthos was estimated at 3,600 organisms/mA? with an ash-free dry weight of about 2.2 g/mA? (about 33 kg/hectare dry weight). Estimated biomass was 1.3 g/mA? (about 18.5 kg/hectare dry weight) and depths of 0.5-10 m and 3.5 g/mA? (about 52.5 kg/hectare dry weight) at greater depths.